Brush‐Paintable, Temperature and Light Responsive Triple Shape‐Memory Photonic Coatings Based on Micrometer‐Sized Cholesteric Liquid Crystal Polymer Particles

Abstract

In this work, light and temperature responsive, brush‐painted photonic coatings exhibiting three different colored and surface topographical states are reported. The different states arise from the use of cholesteric liquid‐crystalline micrometer‐sized polymer particles as shape‐memory photonic pigments that are dispersed in a shape‐memory binder. The first temporal state is induced by compressing the photonic particles at high temperature, resulting in blueshift of the structural color. The second temporal state is obtained by embossing a diffractive grating on the surface at an intermediate temperature leading to a relief topography and a rainbow optical effect. Both optical and surface topographical changes coexist and are stable at room temperature until they are reverted independently either by heating or locally by light illumination. Multicolored paints that reflect selectively left‐handed or right‐handed polarized light are developed to create arbitrary polarization‐dependent multicolor and topographical brush‐painted patterns. These temperature and light responsive triple shape‐memory photonic paints have potential applications as battery‐free optical sensors, responsive decoration, and smart adhesives.

Mechanochromism in Structurally Colored Polymeric Materials

“…It can be argued that these advances will be particularly impactful in the context of mechanosensing: such beads could be dispersed in different polymeric matrices, which obviates the restrictive requirements for fine nanoscale ordering on the matrix and fabrication approach, potentially widening the scope of these materials as mechanosensors. [85,89,179] Increasingly, researchers are introducing other functionalities to photonic or plasmonic polymers, drawing from diverse areas of material science: examples include supramolecular selfhealing, [256] shape memory, [245,[250][251][252]257] and tunable moduli. [178] These designer materials could be particularly useful in areas such as soft robotics or electronic skins, [63,258,259] where polymeric components with bright, tunable color and the ability to self-repair for an improved product lifetime are highly desirable.…”

“…Detailed mechanographs can be produced by imaging with a camera or microscope; recently, hyperspectral cameras have been used to extract spatially resolved spectral information, as a more precise measure of the material response than RGB values. [226] Structurally colored polymers are frequently used to visualize and examine the highly inhomogeneous strain distributions induced by the indentation of flat samples against a surface [41,48,49] and free membranes, [37,43,226] or by more com-plex indenters such as stamps [42,43,47,50,69,179] and fingerprints, [34] highlighting their potential in security applications. Localized regions of tension and compression in the same sample can also be visualized, for instance, in three-point bending.…”

“…[246] Holograms made from patterned gratings of this material could be mechanically erased under compression and thermally restored. Thin films or coatings of structurally colored shape memory materials that exhibit mechanochromism have been made from inverse opals, cholesteric liquid crystalline polymers [179,247,248] or blue-phase liquid crystalline polymers. [187] These materials can be programmed in a similar way using thermal stimuli.…”

“…In addition to thin films, microspheres of CLC elastomers can be produced by polymerizing emulsion droplets containing monomeric mesogens, with the LC ordering induced from the oil–water interface. [ 179 ] In addition to offering the possibility of increased production volumes of mechanochromic CLC materials, these pigments can also be dispersed in a wide range of different polymeric matrices, broadening their range of potential applications. For example, mechanochromic shape memory coatings were prepared by dispersing the photonic microspheres, measuring ≈10–50 µm in diameter and with T g,spheres = 67 °C, in bisphenol‐A based ethoxylate diacrylate, which was then photopolymerized to give a film with T g,matrix = 38 °C.…”

Intelligent Polymer‐Based Bioinspired Actuators: From Monofunction to Multifunction

“…Structural colorations, arisen from the optical interference, diffraction, and reflection by unique micro‐/nanostructures [ 76 ] and showing highly stable colors, [ 77 ] have therefore been introduced for the design and fabrication of the bioinspired color‐shifting actuators with enhanced sensing and reporting functions. Through combining stimuli–responsive polymers with periodically ordered structures, various bioinspired actuators enabling color shifting in response to different stimuli (e.g., humidity, [ 78 ] organic vapors, [ 79 ] temperature, [ 80 ] light, [ 81 ] and magnetic field [ 82 ] ) have been prepared based on the adjustable structural colorations, showing great versatility in sensing and reporting different environmental signals. As a minor change in the structure can lead to significant color changes for the bioinspired color‐shifting actuators based on the structural colorations, these actuators have shown superior sensitivities in sensing and can even report the changes in cell traction force.…”